To use power measurements from an emonTX and rfm12pi with Python:

The modules from openenergymonitor.org are great but getting them working is not easy. Hopefully this will help -


• Purchase an rfm12pi, a current transformer (or three) and an emonTX kit, solder the emonTX together and upload your chosen firmware to it.
  
  


• Plug the current transformer into the emonTX, clamp it around a neutral or live cable and power the emonTX.

On the Raspberry Pi -

• sudo nano /boot/cmdline.txt
  and remove the line
  console=ttyAMA0,115200 kgdboc=ttyAMA0,115200
• sudo nano /etc/inittab
  remove the line towards the bottom
T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100
• install Python Serial:
  sudo apt-get install python-serial
• Plug the rfm12pi onto the Raspberry Pi
  
• The output from the emonTX is something like:
  10 201 1 25 0 28 0 4 13
  which is the node number, CT1, CT2, CT3 and tempreature in the form of:
  10 201+(1*256) 25+(0*256) 28+(0*256) 4+(13*256)
  And the serial connection between the RFM12pi uses port /dev/ttyAMA0 at 9600 kbps
  So running a Python script somthing like the following should give you some meaningful output:
  
  #! /usr/bin/python
  
  # serial monitor for emonTX (current only) plus RFM12pi
  
  import serial
  
  # setup the serial port
  
  ser = serial.Serial("/dev/ttyAMA0", 9600)
  ser.bytesize = serial.EIGHTBITS
  ser.parity = serial.PARITY_NONE
  ser.stopbits = ser.STOPBITS.count(1)
  ser.timeout = 10
  
  while True:
  ser.open()
  c = ser.readline()
  try:
  c = bytes.decode(c)
  except:
  c = 'Decode Error'
  
  # print the whole thing
  print (c)
  
  # work out the (apparent) power and print it
  n = c.split(" ")
  power = int(n[2])+(256*int(n[3]))
  print "Apparent Power = ", str(power)
  print ""
  
  ser.close()


• Calibration ? must look into it.
• Clock with power monitor ... work in progress.